Freeze drying apparatus



Nov. 22, 1966 u. HACKENBERG 3,286,365

FREEZE DRYING APPARATUS Filed April 5, 1964 2 Sheets-Sheet l i@ 9////////////a/{/\/////////: a 7

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FREEZE DRYING APPARATUS Filed April 5, 1964 2 Sheets-Sheet 2 Ivezzow.-I/iiaa Hauff/323218243 United States Patent O L 44,5 Claims. (Cl. 34-92)This invention relates to freeze drying apparatus and more particularlyto apparatus for freeze drying material in containers which are sealedafter the process and used as packages for the dried material.

Freeze drying is a well-known process in which a material to be dried isfirst frozen and then placed inside an evacuable chamber. Water vaporremoval apparatus, such as, for example, a deep-cooled ice condenser,then absorbs sublimating Water vapor produced by heating of the frozenmaterial. A predetermined low pressure is continuously maintained withinthe vacuum chamber during the drying process by means of conventionalvacuum pumps communicating with the chamber.

A technical problem in the freeze drying of foods resides in theapplication of sublimation inducing heat to the frozen product. Theproblem is one of providing the lgreatest possible food throughput in agiven installation. This implies maximum use of the space availablewithin the vacuum chamber and lowest possible drying times. However, inorder to avoid heat damage to the drying product, certain limitations-as to maximum applied heating temperatures and/ or space utilizationmust be maintained.

One method of freeze drying utilizes heaters to radiantly heat thematerial being dried. To obtain effective radiant heat transfer, thetemperature of the heaters must be substantially greater than that ofthe product surface. Normally this temperature is greater than thatpermissible to prevent heat damage of the product (for most products themaximum heat is between 40-80 C.). The drying time must be very short sothat the drying surface of the product is not subjected to radiant heatdamage. Therefore, only very shallow layers of product material whichwill dry quickly can be safely used. The loading capacity for systems ofthis kind is normally limited to about 10 kilograms per square meter.

Another method of applying heat in freeze-drying applications is byconduction or lconvection from heaters to the frozen product. In thiscase the material to be dried is maintained as close as possible to theheat source so as to provide the best possible heat transfertherebetween. One embodiment of this method utilizes product containerswhichare directly heated (for example, by electricity, steam, etc.) soas to function as the heat source. The disadvantages of this embodimentreside in the mechanical difiiculties of supplying evenly distributedheat energy to the product containers. The diiiiculties are accentuatedby the fact that the product containers are normally adapted for removalfrom carrier racks, conveyors, etc., so as to permit ease of producthandling, container cleaning, etc.

Another embodiment utilizes product trays adapted to contact stationaryheating plates. In this embodiment the diiiiculty resides in the poorheat transfer through the minute vacuum spaces between the heated platesand the adjacent product containers. The poor heat transfer prevents theattainment of the same temperature in the containers that exists in theheating plates. Thus the plates must be operated above maximumpermissible product temperature so as to establish the maximum in theproduct containers. However, this is also objectionable, since mostfreeze-drying installations in the interest of efficient ICC spaceutilization include interleaved layers of product and heat sources. Thusthe product in the containers (uncovered to allow escape of water vapor)is subject to the excessive radiant heat of the heater plate positioneddirectly above the container.

Another factor which greatly affects production costs in the freezedrying of many materials, especially food products, is the excessivehandling of both the product and the product containers used during theprocess. The product must be prepared for freezing, placed into dryingcontainers, loaded into a freeze dry installation before the process canbegin. Then upon completion of the freeze drying process the driedmaterial must be removed from the drying containers and packed intodifferent packages for commercial distribution. For many products, thisfinal packaging is complicated by the requirement that the packaging bevacuum tight and accomplished in an inert atmosphere such as, forexample, a nitrogen atmosphere. Upon completion of one drying cycle thedrying containers, which have frequently been quite soiled by burnedproduct, must be thoroughly washed and dried before reuse.

It is, therefore, the object of this invention to provide a freezedrying apparatus which greatly reduces the requirements for product andcontainer handling and in addition permits efficient transfer of heat tothe drying product during the freeze drying process without danger ofproduct heat damage.

One feature of this invention is the provision of an irnproved freezedrying installation which comprises heating plates for furnishingconduction heating to the product being dried, a product housing adaptedto shield the product from direct heat radiation and to permit escape ofsublimating water vapor, and an additional product container adapted forplacement Within the product housing thereby -allowing use of theadditional container as the final packaging for the dried product.

Another feature of the invention is the provision of a freeze dryinginstallation of the above featured type in which the product housing isconstructed of metal Walls having a thickness of at least l millimeterso as to exhibit good heat conduction properties.

Another feature of this invention is the provision in a product housingof the above featured type vof optically dense water vapor escapeopenings which shield the product from direct heat radiation.

These and other objects and features of the present invention willbecome apparent upon a perusal of the following description taken inconjunction with the accompanying drawings wherein:

FIG. l is a cross sectional view of a segment of the freeze dryinginstallation according to the present invention;

FIG'. 2 is a side view partially in cross section of the product housingshown in FIG. l; and

FIG. 3 is a front and side view partially in cross section of anotherproduct housing embodiment of the present invention.

Referring now to FIGS. l and 2 there is shown a vacuum chamber wall 11which encloses a plurality of vertically ribbed heating plates 12. Thevertical central column 13 supports the horizontal bars 14 to which areattached the horizontal angle bars 15. The top wall extensions 16 of therectangular product housing 17 provide shoulders 18 which aredemountably supported by the horizontal angle portions of the angle bars15.

The product housing 17 is divided into Avertical sections 19 by dividerswhich can be either an integral part 21 of the housing or removableparts 22 thereof. Water vapor escape openings 23 are cut in the sidewall of the housing 17 and in a preferred embodiment these openings canbe made optically dense by providing a directional change as shown inthe openings 24. Supported in the vertical sections 19 by the bottomwall of housing 17 and dividers 21, 22 are the tray containers 25 lledwith a product 26 to be dried. The containers are passed into thehousing 17 through the open ends 27 thereof.

During operation of the apparatus according to the invention shown, thecontainers 2S are lled with a frozen product 26 to be dried and placedin the housing 17. After the loaded housing 17 has been positionedwithin the vacuum chamber, the chamber is evacuated to a pressure ofabout -1 mm. Hg and the heater plates 12 are energized.

The top, bottom and side walls of the housing 17 shield the product 26from direct heat radiation from the heating plates 12 while the open endwalls 27 and openings 23, 24 permit escape of sublimating water vaporfrom the frozen product. The walls of the housing 17 are preferablycomposed of metal and have a thickness of at least 1 mm. (preferablyabout 2 mm.) so as to provide a good heat conduction path to thecontainers 25 and product 26. Upon completion of the freeze dryingprocess, the containers 25 still filled Iwith the dried product can besealed in a gas tight manner by suitable sealing equipment (not shown).This sealing can be preformed in anl inert atmosphere if so desired. Thecompletely packaged product is then ready for commercial distribution.The housing assemblies 17 are immediately available for reuse withoutany cleaning requirement since they have not been in direct contact withthe product itself.

FIG. 3 shows another product housing embodiment of the presentinvention. The structure is similar to that shown in FIGS. 1 and y2except that end walls 31 rare closed and contain vapor escape openings32. Also the side walls 33 are demountable and do not extend completelyto the top of the housing 17 leaving a vapor escape slot 34. Theoperation of this embodiment is the same as for that shown in FIGS. 1and 2 except that the containers 25 are loaded into the housing 17before the side walls 33 are attached with bolts 35.

Thus the present invention provides a freeze drying installation whichefliciently heats the drying product without radiation damage and alsogreatly reduces the amount of product and product container handlingrequired during the process. The invention is particularly suited forthe preparation of freeze dried food products, especially completefreeze dried dinners.

Obviously many modiiications and variations of the .present inventionare possible in the light of the above teachings. It is, therefore, tobe understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically described.

What is claimed is:

1. An apparatus for the freeze drying of moisture containing materialcomprising a vacuum chamber, heating means positioned Within said vacuumchamber, housing means positioned within said vacuum chamber `adjacentsaid heating means, a plurality of means adapted to be filled with amaterial to be freeze dried, said container means being removablypositioned within said housing means and having an opening to permit theescape of Water vapor therefrom, said housing adapted to completelyshield the material contained in said container means from direct heatradiation from said heating means, and wherein said housing meanscontains an opening which permits escape of Water vapor from thematerial contained in said container means.

2. The apparatus according to claim 1 wherein said housing means isremovably supported within said vacuum chamber.

3. The apparatus according to claim 1 including divider means whichseparate said housing means into vertical sections and wherein saidcontainer means comprise individual containers positioned in each ofsaid vertical sections.

4. The apparatus according to claim 3 wherein said housing means isremovably supported within said vacuum chamber.

5. The apparatus according to claim 1 wherein said housing means isformed by metal walls having a thickness of at least 1 mm. therebyproviding for good heat conduction.

6. The apparatus according to claim 5 including divider means whichseparate said housing means into vertical sections and wherein saidcontainer means comprise individual containers positioned in each ofsaid vertical sections.

7. The apparatus according to claim 6 wherein said housing means isremovably supported Within said vacuum chamber.v

8. The apparatus according to claim 5 including a de mountable covermeans which at least partially covers the opening in said housing means.

9. The apparatus according to claim 8 including divider means whichseparate said housing means into vertical sections and wherein saidcontainer means comprise individual containers positioned in each ofsaid vertical sections.

10. The apparatus according to claim 9 wherein said housing means isremovably supported within said vacuum chamber.

References Cited by the Examiner UNITED STATES PATENTS 3,174,229 3/1965Stokes et a1. 34a-236 FOREIGN PATENTS 936,054 s/1963 GreatBrirain.

OTHER REFERENCES German printed application 1,102,653, March 1961.German printed application 1,119,773, December 1961 ROBERT A. OLEARY,Primary Examiner.

W. E. WAYNER, Assistant Examiner.

1. AN APPARATUS FOR THE FREEZE DRYING OF MOISTURE CONTAINING MATERIALCOMPRISNG A VACUUM CHAMBER, HEATING MEANS POSITIONED WITHIN SAID VACUUMCHAMBER, HOUSING MEANS POSITIONED WITHIN SAID VACUUM CHAMBER ADJACENTSAID HEATING MEANS, A PLURALITY OF MEANS ADATPED TO BE FILLED WITH AMATERIAL TO BE FREEZE DRIED, SAID CONTAINER MEANS BEING REMOVABLYPOSITIONED WITHIN SAID HOUSING MEANS AND HAVING AN OPENING TO PERMIT THEESCAPE OF WATER VAPOR THEREFROM, SAID HOUSING ADAPTED TO COMPLETELYSHIELD THE MATERIAL CONTAINED IN SAID CONTAINER MEANS FROM DIRECT HEATRADIATION FROM SAID HEATING MEANS, AND WHEREIN SAID HOUSING MEANSCONTAINS AN OPENING WHICH PERMITS ESCAPE OF WATER VAPOR FROM THEMATERIAL CONTAINED IN SAID CONTAINER MEANS.